Insulating oil compositions



, romeo Feb 59 a,

ostrichsrh res es eschew roman p 955mg HNSMTHNG cowosimoms 1 (Charles ill. Boomers, East ldcKeesport, rah, can signer to Gull Research to Development Cornwere No Brewing.

. y, lPittehmgh, re, a. corporation or Belo Ap lication member to, recs, Serial Elm-428,399 I 3 (Claims. (Cl. 174-417) This invention or discovery reletes to insulat lng oil compositions; and it comprises such a. composition, particularly e. transformer oil, highly resistant to deterioration by orddetion, includ ing a petroleum 011 containing a. small amount or an alkyl ester of an emino-benzoic-acid, edvahtcgeously. methyl snthranilste' and other short chain allryl esters or ortho-amino-benzoic sold; all as more fully hereinafter set forth and escloimed. 7

In mony types of electrical transformers the core and windings are immersed in a suitable petrolcum oil, for servin as a. dielectric and for heat away from the core and windings' Transformer oils are distillate oils refined in such manner as to secure the specified characteristics to great an extent as possible. Achievement of satisfactory oxidation resistance is di'idcult, for while ozddotionol cheluges ere slow, transformer oils are ordinarily expected to remain in service over long periods. Gridstionol cheeses result in the formation of insoluble matter or sludge. The sludge tends to render the all more miscible with water, with production of emulsions in the presence of condensed water and a. consequent degradation of the dielectric prop erties of the oil body. The sludge also deposits on the windings and core with reduction of the eidciency of heat transfer. Oxidation of trens= former oils tends to be promoted by contact with metals, especially copper, and with the usual varnishes and insulating materials.

. Various materials have been "proposed for incorporation into-transformer oils with the object of inhibiting oxidation, and some of these have come into use. The usual anti-oxidants may be divided in two principal classes: (1) those 'which are associated with a lengthenlng'of the induction period, that is the time which elapses before appearance of sludge in the oil'subject to oxidation, and (2) those which reduce the amount of sludge formed per day after it once begins to form. In evaluating oils containing anti-oxidants, the most useful criterion is a value which takes into account both these characteristics, via,

form a definite amount of sludge, say 0.1 per cent by weight of the oil.

I have discovered s. new class of antiomdent compounds which bring about both a. lengthening of the induction period and a. marked lessening of the rate of sludge formation thereafter, when incorporated in transformer oils in even minimal amounts. These antioxidants have certain other advantages. They are quite soluble in oil, more so then many other antioxidants, but ere highly insoluble in water, thereby minimizing the tendenc'y to form aqueous emulsions. Also they are hoe-acid and do. not deleterlously afloat the acid number of the transformer oil when incorporated therein.

These antioxidant compounds are skid esters of on amino beuzcic ecid which can he repre sented by the sh'uctmol is his:

mowing-ca ing 2. short chain allwl mic-up, pestle Y of ortho emino-hehzoic acid, are advantage They are very efieotive in precehdng or rate d ing sludging and other orddsfionsl of the ch. 7

In the preferred embodhnents or" this invention, the antioxidants employed are esters of ortho-emino-benzoic acid which can he repre= sentedby the structural formula:

- wherein R is :2. short chain alkyl group; these esters being also as alkyl enthrenilstes. For instance, methyl ahthranilate is on advantageous antioxidant in transformer oils and other insulating oil compositions. It is readily soluble in transformer oils and when incorporated in even minimal amounts efiectively inhibits sludge the time required, under thetest conditions, to lo purposes.

alkyl anthranilates. Nevertheless, they are sufficiently soluble for the present purposes and improve theresistance of the oil to oxidational deterioration.

In the broad practice of this invention, insulating oils such as transformer oils and the like can be advantageously improved by incorporating alkyl esters which can be generically represented by the structural formula:

wherein R represents a short chain alkyl group.

These compounds or antioxidants when added to transformer oils or-other electrical insulating oils in small amounts, advantageously amounts corresponding to about 0.05 to 0.5 per cent by weight of the .oil, effectively stabilize such oils against oxidational deterioration. For instance,

the beneficial eifect may be obtained with amounts as small as 0.01 per cent. In such amounts they are readily soluble in such oils.

In the following table comparative oxidation test resultsare set forth for oils containing these new antioxidants, for an untreated oil and for certain other antioxidants not. a part .of the invention. .The test data reported in the table were obtained in accordance with the sludge. formation test for mineral transformer-oils described by I". M. Clark and E. A. Snyder in their paper entitled "Testing for Sludge Formation in Mineral Transformer Oil presented at the Thirty-ninth Annual Meeting for the American Society for Testing Materials. The test procedure described in the aforesaid paper was developed in collaboration with the laboratories of a considerable number of firms engaged in oil refining and in the manufacture of electrical equipment,

In this test, samples of oil are maintained in tubes containing copper wire at a constant temperature of approximately 120 C. The tubes are open at the top to an enclosed air space and dry air is passed at a controlled rate of 1 to 2 cubic feet per hour through the enclosed space above the sample tubes. Into each tube nilate.m'ay be used in with-an al-- is introduced 22 grams of oil or oil composition to be tested, a number of tubes being employed. At prescribed intervals the tubes are successively removed and the amount of .sludge determined;

The results of these tests are reported in terms of the induction period, the percent of sludge formed per day and the ,total number of days taken to form 0.1 per cent of sludge.

The oil employed in all ofthe tests set forth hereinbelow'was a typical petroleum transformer oil, commonly used for the purpose indicated. The addition, agents employed were as follows:

Methyl anthranilate, designated as MA I Ethyl anthranilate, designated as EA" Methyl-p-amino benzoate, designated as MP Anthranilic acid, designated as A" 2:6-di-tertiary-butyl 4 -methyl phenol. designated as OP The results of tests on the base oil alone and the same oil containing the above-mentioned addition agents are given in the following table:

' B ots of T m Inducs format to Test Transformer Oil tlon No. composition 2 g u percent per days 0. 5 0. 0100 ll] a 0 0. 0047 9;; z 0 0. 0034 a: 9.0 0. 0015 70 a o 0. 0015 10 Oil-+0.3 Z 0 0. 0027 40 Oil-{411% 0. 0 0. M 12 s. 0u+0.1% 0.0 0.0041 22 9 Oil-H137 OF 12. 5 0. 0205 18 10 Oil-{ 0.05% MA and 0.3% 10.0 0.0047 32 n Olga-9.3% MA and 0.3% a. 0 0. 0035 30 In the table, tests 2 to '7; inclusive, l0 and 11 relate to improved insulating oil compositions contemplated in tins-invention; the oil compositions tested being improved transformer oils containing a short chain alkyl ester of amino-benzoic acid. For purposes of comparison tests on the transformer oil alone i 1) and on the oil containing anthranilic acid (8) and '2,6-\di-tertiarybutyl-4-methyl phenol (9) have been included in the table.

As indicated in tests 2 to 5, inclusive, the benefits obtained with methyl anthranilate increase with proportions thereof up to around 0.5 per cent. In most cases the further increase does not further reduce the oxidation sensitivity of the 011. As methyl anthranilate ives good results, it is ordinarily employed in the practice of the present invention.

However, as shown ante, other short chain alkyl anthranilates are likewise effective and may be also used to improve transformer oils. For instance; as shown in test 6, ethyl anthranilate produces similar improvements. The use of alkyl esters of other amino benzoic acids .is illustrated in test '1 wherein the antioxidant is the methyl ester of para-amino-benzoic acid and like improved results are obtained. Further, these alkyl esters of amino-benzoic acids may be used in conjunction with other improvement agents; they being compatible and miscible with such agents and oil compositions containing the same, as well as soluble in oil alone. This is illustrated in tests 10 and 11 wherein methyl anthrakylated' phenol having antioxidant properties, specifically 2:6-di-tertlary-lmtyl-4-methylv phenol. As there shown improvements are obtained which are not, obtainable with either of these agents. This is evident from given ante. s

While this invention has been described herethe test results in with particular reference to transformer oil the scope of this alkyl anthranilate having the following formula wherein R represents a short-chained alkyl roup selected from the class consisting of methyl and ethyl groups, the amount of said shortchained 'alkyl anthranilate being suilicient to render the petroleum oil resistant to sludging and other oxidational deterioration.

2. In the operation of electrical transformers containing a petroleum oil as the dielectric and cooling medium, the improvement which comtaining 0.01 to 0.5 per cent by weight of methyl anthranilate dissolved therein, the amount of methyl anthranilate being sufl'lcient to render the petroleum oil resistant to sludging and other oxidational deterioration.

3. In the operation of electrical transformers containing a petroleum oil as the dielectric and cooling medium, the improvement which'comprises insulating and cooling the'windings and core of a transformer with a petroleum oil containing 0.01 to 0.5 per cent by weight of ethyl anthranilate dissolved therein, the amount of ethyl anthranilate being sufficient to render the petroleum oil resistant to sludging and other prises insulating and cooling the windings and I5 oxidational deterioration.

core of a transformer with a petroleum oil con- CHARLES E. TRAUTMAN. 

